Thin film device and its fabrication method

ABSTRACT

A thin film device includes a metal sulfide layer formed on a single crystal silicon substrate by epitaxial growth; and a compound thin film with ionic bonding, which is formed on the metal sulfide layer by epitaxial growth. Alternatively, a thin film device includes a metal sulfide layer formed on a single crystal silicon substrate by epitaxial growth; and at least two compound thin films with ionic bonding, which are formed on the metal sulfide layer by epitaxial growth. For example, (11{overscore (2)}0) surface AlN/MnS/Si (100) thin films formed by successively stacking a MnS layer (about 50 nm thick) and an AlN layer (about 1000 nm thick) on a single crystal Si (100) substrate, are used as a substrate, and a (11{overscore (2)}0) surface GaN layer (about 100 nm thick) operating as a light emitting layer is formed on the substrate, thereby fabricating a thin film device.

[0001] This application claims priority from Japanese Patent ApplicationNo. 2002-276205 filed Sep. 20, 2002, which is incorporated hereinto byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a thin film device including acompound having ionic bonding (called “ionic crystal” from now on) andits fabrication method, and more particularly to a thin film device andits fabrication method preferably applicable to electronic devicesutilizing an ionic crystal thin film as a functional film, such as ahigh brightness blue light emitting device (semiconductor laser), metalinsulator semiconductor field effect transistor (MISFET), high electronmobility transistor (HEMT) and thin film capacitor.

[0004] 2. Description of the Related Art

[0005] Nitride, oxide and sulfide each exhibit a variety of physicalproperties. Although they are valuable functional materials aspolycrystalline, their single crystals can become more effective orexhibit new characteristics. When applying these materials to thin filmdevices, forming their single crystal thin films can implement highperformance, high function devices unachievable by polycrystalline thinfilms.

[0006] For example, consider devices using nitride thin films such as ahigh brightness blue light emitting device using GaN thin films, aMISFET using AlN/GaN thin films and a HEMT using AlGaN/GaN thin films.Although a variety of such devices have been proposed and implemented,unless the nitride thin films consist of single crystal thin filmswithout little lattice defects or grain boundary, their carrier mobilitycan be reduced, or the light emitting efficiency of their light emittinglayers or their lifetime can be reduced.

[0007] As for the single crystal thin films, it is common that they areepitaxially grown using a single crystal substrate. For example, therehave been reported that GaN-based single crystal thin films are formedon a single crystal sapphire substrate by an MOCVD (Metal OrganicChemical Vapor Deposition) method or by a gas source MBE method(Molecular Beam Epitaxial Method), or on a SiC substrate by a lowpressure metal organic vapor phase epitaxy (see, Kiyoteru Yoshida“Electronic devices using GaN” OYOBUTURI Vol.68, No.7, pp.790 and 798,published by The Japan Society of Applied Physics, Jul. 10, 1999). Asfor the oxide-based single crystal thin films, their epitaxial thinfilms are formed on a substrate composed of single crystal strontiumtitanate (SrTiO₃: STO), single crystal lanthanum aluminate (LaAlO₃:LAO)or single crystal sapphire substrate by a sputtering or PLD method(Pulsed Laser Deposition).

[0008] However, since the sapphire substrate, SiC substrate, singlecrystal STO substrate and single crystal LAO substrate are expensive, itis preferable that the thin films be formed on a general purpose Sisubstrate. In addition, from the viewpoint of a merger with Si devices,it is preferable that the functional thin films be epitaxially grown ona Si substrate. However, it is difficult to epitaxially grow an ionicbonding thin film directly on a Si single crystal substrate. The reasonfor this is considered that since the silicon is a covalent crystal, amaterial with a lattice constant differ from that of Si by a few percentcannot grow coherently (pseudomorphically) on a substrate, therebyleaving lattice defects.

[0009] As a method of forming a thin film on a Si single crystalsubstrate, a method of inserting a buffer layer is known.

[0010] A commonly used method is to form a metal oxide of CeO₂, Y₂O₃,ZrO₂ and the like, which are more susceptible to oxidation than Si,thereby preventing non-crystalline (amorphous) SiO₂ from beinggenerated. However, it is unavoidable that the Si surface undergoesoxidation, which offers a problem of degrading the film characteristicof the buffer layer formed on the SiO₂. In addition, a buffer layerusing TiN or TaN also has a problem of forming SiN_(x).

[0011] To cope with this, a method using a metal sulfide thin film asthe buffer layer is proposed (see, Japanese Patent Application Laid-openNo.2002-003297). According to the relevant document, the formationGibbs' energy of forming the Si sulfide is rather small. Thus, when itslattice constant is close to that of Si, it is possible to epitaxiallygrow the sulfide without forming an amorphous layer on an interfacebetween the buffer layer and Si. The Japanese Patent ApplicationLaid-open No.2002-003297 discloses that the elements such as Al, Ba, Be,Ca, Ce, In, La, Li, Mg, Mn, Mo, Na, Sr, Ta and Zr have the formationGibbs' energy greater than Si in forming the sulfide, and that using asulfide composed of one of them or a combination of them can suppressthe Si interface reaction, and proposes an oxide thin film device andits fabrication method using the metal sulfide layer as the bufferlayer.

[0012] Furthermore, CdS and ZnS also have the formation Gibbs' energygreater than that of Si in forming the sulfide.

[0013] However, a thin film device including epitaxial thin films for alaser diode or LED formed on a Si substrate, and its fabrication methodhave not been implemented.

SUMMARY OF THE INVENTION

[0014] An object of the present invention to provide a thin film devicehaving a metal sulfide epitaxial thin film formed on a Si substrate whenfabricating a compound thin film device with ionic bonding on a Sisingle crystal substrate, and a fabrication method of the thin filmdevice having the epitaxial thin film formed. As a result of a newresearch, the applicants have found that it is possible to epitaxiallygrow a sulfide thin film other than ZnS on a Si substrate, and toepitaxially grow on its surface an ionic crystal other than an oxide.

[0015] According to a first aspect of the present invention, there isprovided a thin film device comprising: a metal sulfide layer formed ona single crystal silicon substrate by epitaxial growth; and a compoundthin film with ionic bonding, which is formed on the metal sulfide layerby epitaxial growth.

[0016] According to a second aspect of the present invention, there isprovided a thin film device comprising: a metal sulfide layer formed ona single crystal silicon substrate by epitaxial growth; and at least twocompound thin films with ionic bonding, which are formed on the metalsulfide layer by epitaxial growth.

[0017] According to a third aspect of the present invention, the metalsulfide layer in the first or second aspect of the present invention maybe composed of one of a manganese sulfide (MnS), magnesium sulfide(MgS), and calcium sulfide (CaS).

[0018] According to a fourth aspect of the present invention, the metalsulfide layer in the first or second aspect of the present invention maybe composed of a material whose chemical formula is given byZn(1−x)M_(x)S_(y), in which part of zinc of zinc sulfide (ZnS) issubstituted by another metal (M), where x and y are values between 0 and1.

[0019] According to a fifth aspect of the present invention, the metalsulfide layer in the fourth aspect of the present invention may becomposed of zinc manganese sulfide ((Zn, Mn)S).

[0020] According to a sixth aspect of the present invention, the metalsulfide layer in the first or second aspect of the present invention maybe composed of a material whose chemical formula is given by Zn(1−x)(M,N, . . . )_(x)S_(y), in which part of zinc of zinc sulfide (ZnS) issubstituted by other metals (M, N, . . . ), where x and y are valuesbetween 0 and 1.

[0021] According to a seventh aspect of the present invention, the thinfilm device in the first or second aspect of the present invention mayfurther comprise a platinum group layer formed between the metal sulfidelayer and the compound thin film by epitaxial growth.

[0022] According to an eighth aspect of the present invention, a metalof the platinum group layer in the seventh aspect of the presentinvention may be one of rhodium, iridium, palladium and platinum or analloy of them, and the platinum group layer may be composed of a singlelayer or multi-layer thin film thereof.

[0023] According to a ninth aspect of the present invention, thecompound thin film in any one of first to eighth aspect of the presentinvention may be composed of a metal nitride thin film.

[0024] According to a tenth aspect of the present invention, thecompound thin film in any one of first to eighth aspect of the presentinvention may be composed of a metal oxide thin film.

[0025] According to an 11th aspect of the present invention, thecompound thin film in any one of first to eighth aspect of the presentinvention may be composed of a metal sulfide thin film.

[0026] According to a 12th aspect of the present invention, there isprovided a thin film device comprising: a manganese sulfide (MnS) layerformed on a single crystal silicon (100) substrate by epitaxial growth;and an aluminum nitride (AlN) layer formed on the manganese sulfidelayer by epitaxial growth, the aluminum nitride (AlN) layer having a(11{overscore (2)}0) surface as its top surface.

[0027] According to a 13th aspect of the present invention, the thinfilm device in the 12th aspect of the present invention may furthercomprise a compound thin film with ionic bonding, which has a(11{overscore (2)}0) surface formed by epitaxial growth as its topsurface, and is formed on the aluminum nitride (AlN) layer having the(11{overscore (2)}0) surface as its top surface, or via anotherintermediate layer.

[0028] According to a 14th aspect of the present invention, the compoundthin film in the 13th aspect of the present invention may be composed ofa gallium nitride (GaN) thin film having a (11{overscore (2)}0) surfaceas its top surface.

[0029] According to a 15th aspect of the present invention, there isprovided a fabrication method of a thin film device comprising the stepsof: epitaxially growing metal sulfide on a single crystal siliconsubstrate by feeding molecular metal sulfide on the single crystalsilicon substrate under a reduced pressure; and epitaxially growing acompound thin film with ionic bonding on the metal sulfide.

[0030] According to a 16th aspect of the present invention, there isprovided a fabrication method of a thin film device comprising the stepsof: epitaxially growing metal sulfide on a single crystal siliconsubstrate by feeding molecular metal sulfide on the single crystalsilicon substrate under a reduced pressure; and epitaxially growing atleast two compound thin films with ionic bonding sequentially on themetal sulfide.

[0031] According to a 17th aspect of the present invention, there isprovided a fabrication method of a thin film device comprising the stepsof: epitaxially growing a metal sulfide layer on a single crystalsilicon substrate by feeding molecular manganese sulfide on the singlecrystal silicon substrate under a reduced pressure; epitaxially growingan aluminum nitride (AlN) layer having a (11{overscore (2)}0) surface asits top surface; and forming on the aluminum nitride layer a galliumnitride (GaN) thin film having a (11{overscore (2)}0) surface as its topsurface.

[0032] According to an 18th aspect of the present invention, there isprovided a fabrication method of a thin film device comprising the stepof sequentially stacking a metal sulfide layer epitaxially grown on asingle crystal silicon substrate, and at least two compound thin filmswith ionic bonding, which are epitaxially grown on the metal sulfidelayer.

[0033] According to a 19th aspect of the present invention, there isprovided a fabrication method of a thin film device comprising the stepsof: forming a metal sulfide layer on a single crystal silicon substrateby epitaxial growth; forming a platinum group layer on the metal sulfidelayer by epitaxial growth; and forming a compound thin film ionicbonding on the platinum group layer by epitaxial growth.

[0034] According to a 20th aspect of the present invention, the compoundthin film in any one of 15th, 16th, 18th and 19th aspects of the presentinvention may be composed of a metal nitride thin film.

[0035] According to a 21st aspect of the present invention, the compoundthin film in any one of 15th, 16th, 18th and 19th aspects of the presentinvention may be composed of a metal oxide thin film.

[0036] According to a 22nd aspect of the present invention, the compoundthin film in any one of 15th, 16th, 18th and 19th aspects of the presentinvention may be composed of a metal sulfide thin film.

[0037] The above and other objects, effects, features and advantages ofthe present invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a cross-sectional view showing a structure of an AlNsubstrate and GaN thin films formed thereon to construct a GaN lightemitting device in accordance with the present invention;

[0039]FIG. 2A is a graph illustrating characteristics of XRD (X-raydiffraction) measurement results of MnS/Si (111) thin films;

[0040]FIG. 2B is a graph illustrating characteristics of XRD measurementresults of MnS/Si (100) thin films;

[0041]FIG. 3 is a graph illustrating characteristics of XRD measurementresults of AlN/MnS/Si (111) thin films;

[0042]FIGS. 4A and 4B are graphs illustrating characteristics of XRDmeasurement results of AlN/Si (100) thin films;

[0043]FIGS. 5A, 5B and 5C are graphs illustrating characteristics of XRDmeasurement results of AlN/MnS/Si (100) thin films;

[0044]FIG. 6A is a view illustrating RHEED (reflection high electronenergy diffraction) observation results of MnS/Si (100) thin films;

[0045]FIG. 6B is a view illustrating RHEED observation results ofAlN/MnS/Si (100) thin films;

[0046]FIG. 7A is a diagram illustrating simulation results of a RHEEDpattern of a W—AlN (11{overscore (2)}0) surface;

[0047]FIG. 7B is a diagram illustrating simulation results of a RHEEDpattern of an AlN (220) surface with a sphalerite (Wurtzite) structure;

[0048]FIG. 8 is a schematic diagram showing crystal growth orientationrelationships of AlN/MnS/Si (100) thin films;

[0049]FIG. 9 is a view showing a cross-sectional TEM (TransmissionElectron Microscope) image of GaN/AlN/MnS/Si (100) thin films;

[0050]FIG. 10 is a view showing a cross-sectional TEM image of anAlN/MnS interface;

[0051]FIG. 11 is a view showing a cross-sectional TEM image of a GaN/AlNinterface;

[0052]FIG. 12 is a graph illustrating a cathode luminescence lightemitting spectrum of GaN/AlN/MnS/Si (100) thin films at roomtemperature;

[0053]FIG. 13 is a graph illustrating characteristics of XRD measurementresults (2θ-ω) of MgS/Si (100) thin films;

[0054]FIG. 14 is a diagram illustrating characteristics of XRDmeasurement results (pole-figure of MgS (222) peaks) of MgS/Si (100)thin films;

[0055]FIG. 15 is a graph illustrating characteristics of XRD measurementresults (2θ-ω) of MgS/Si (100) thin films;

[0056]FIG. 16A is a graph illustrating characteristics of XRDmeasurement results of (Zn, Mn)S films (Mn is 5%) formed on a Si (100)substrate using a PLD method; and

[0057]FIG. 16B is a graph illustrating characteristics of XRDmeasurement results of (Zn, Mn)S films (Mn is 5%) formed on a Si (111)substrate using a PLD method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0058] The invention will now be described with reference to theaccompanying drawings.

[0059]FIG. 1 is a cross-sectional view showing a structure of an AlNsubstrate and GaN thin films formed thereon, which constitute a GaNlight emitting device in accordance with the present invention. As foran existing GaN-based light emitting device grown on a sapphire (0001)surface, the Stark effect occurs because of internal electric field dueto piezo-electric effect, thereby offering a problem of an adverseeffect on its light emitting characteristics. To solve the problem, oneof conventional techniques grows a GaN (11{overscore (2)}0) surface onthe R surface of the sapphire of the sapphire substrate, and another ofthem grows a cubic GaN on a SiC/Si (100) surface. In contrast, thepresent embodiment employs a Si (100) surface, a commonly usedsubstrate, and forms a Si (100) substrate 1 with an AlN (11{overscore(2)}0) surface capable of utilizing a thermodynamically stable GaN(11{overscore (2)}0) surface. Utilizing the AlN substrate in accordancewith the present invention makes it possible to form the GaN(11{overscore (2)}0) surface inexpensively which is free from theadverse effect of the Stark effect on the light emittingcharacteristics, thereby being able to form the GaN light emittingdevice thereon.

[0060] Such GaN thin films are formed in the following process. Beforedescribing the formation of the GaN (11{overscore (2)}0) surface thinfilm, the formation of a MnS buffer layer 2 on the Si substrate 1 willbe described. A single crystal Si (100) substrate and single crystal Si(111) substrate had their native oxides removed by HF (HydrogenFluoride), followed by being washed with water, placed in a depositionchamber, and drawn to vacuum for about ten minutes. Then, the MnS bufferlayer 2 was formed to a thickness of 20 nm by the PLD method at asubstrate temperature of 700° C. in the vacuum of about 1×10⁻⁶ Torr.

[0061]FIGS. 2A and 2B illustrate XRD measurement results of the MnS thinfilm. The MnS has a cubic NaCl structure with a lattice constant of5.209 Å. The MnS has (111) orientation as illustrated in FIG. 2A when itis formed on the Si (111) substrate, and (100) orientation asillustrated in FIG. 2B when it is formed on the Si (100) substrate.Accordingly, as in the case of forming an ionic bonding epitaxial thinfilm on a Si substrate using ZnS as a buffer layer, using MnS as thebuffer layer will make it possible to epitaxially grow an ionic crystalthin film with a cubic structure on the Si (100) substrate, and ahexagonal ionic crystal thin film on the Si (111) substrate. It is alsopreferable to form on the MnS thin film 2 or ZnS layer, a platinum grouplayer formed by the epitaxial growth, and to form on the platinum grouplayer, a compound thin film with ionic bonding formed by the epitaxialgrowth. One of rhodium, iridium, palladium, platinum or their alloys canbe used to form a single layer film or multi-layer thin film. It is alsopreferable to sequentially stack two or more compound thin films withionic bonding.

[0062] An AlN thin film 3 was formed on the MnS/Si thin film at asubstrate temperature of 700° C. in a nitrogen atmosphere of 5×10⁻⁵Torr.

[0063]FIG. 3 illustrates XRD measurement results when the Si (111)substrate is used. An AlN thin film (W—AlN) of a wurtzite structure isgrown with c axis orientation on the Si (111) substrate, thereby forminga c surface.

[0064] An AlN thin film was formed on the MnS/Si (100) thin film in thesame conditions as those of the AlN thin film of FIG. 3. FIG. 4Aillustrates XRD measurement results. The AlN thin film of the wurtzitestructure with the (11{overscore (2)}0) surface orientation was grown onthe Si (100) substrate. This plane is perpendicular to the c surface.FIG. 4B illustrates, for comparison purposes, XRD measurement results ofan AlN thin film which was directly formed on a Si (100) substratewithout forming the MnS buffer layer. Without the MnS buffer layer, theAlN thin film (W—AlN) of the wurtzite structure is grown with the c axisorientation. Therefore we found it effective to interpose the MnS bufferlayer to form the (11{overscore (2)}0) surface of the AlN thin film onthe Si (100) substrate.

[0065] FIGS. 5A-5C illustrate XRD Phi scan measurement results of theAlN/MnS/Si (100) thin films. It is seen that the cubic MnS isepitaxially grown on the Si (100) substrate, and AlN thin film formedthereon is also epitaxially grown four times symmetrically.

[0066] It is seen from the RHEED (reflection high-energy electrondiffraction) observation that the AlN thin film formed on the MnS/Si(100) thin film by the present fabrication method has a wurtzitestructure rather than a sphalerite structure. The observation resultsare shown in FIGS. 6A and 6B and FIGS. 7A and 7B.

[0067]FIGS. 6A and 6B show patterns when an electron beam is launchedinto the Si[01{overscore (1)}] and Si[010] directions. FIG. 6Aillustrates RHEED observation results of the MnS/Si (100) thin films.They exhibit a streak pattern, and it is seen from the spacing betweenthe acceleration voltage (25 kV) of the incident electron beam and thestreak that the lattice constant of MnS is about 5.2 Å, which nearlyequal to the value 5.209 Å given by the foregoing relevant document(Kiyoteru Yoshida “Electronic devices using GaN”, OYOBUTURI Vol.68,No.7, pp.790 and 798, published by The Japan Society of Applied Physics,Jul. 10, 1999). FIG. 6B illustrates the RHEED observation results of theAlN/MnS/Si (100) thin films in the [{overscore (1)}100] direction and[0001] direction of the AlN thin film, respectively.

[0068]FIG. 7A shows simulation results of the RHEED pattern of the W—AlN(11{overscore (2)}0) surface; and FIG. 7B shows simulation results ofthe RHEED pattern of the AlN (220) surface with the sphalerite (Zincblende: ZB) structure and Wurtzite structure. The pattern analysis showsthat the AlN thin film has a wurtzite structure. The orientationrelationships correspond to the [1{overscore (1)}00] direction and[0001] direction of the AlN thin film along the Si[01{overscore (1)}]direction and Si[010] direction, respectively.

[0069]FIG. 8 is a schematic diagram showing crystal growth orientationrelationships of the AlN/MnS/Si (100) thin films. The orientationrelationships of the thin film growth are AlN [0001] ∥ MnS [010] ∥ Si[010] and AlN [1{overscore (1)}00] ∥ MnS [001] ∥ Si [0011], and planeorientation relationships are AlN (11{overscore (2)}0) ∥ MnS (100) ∥(100).

[0070] It is possible to form the (11{overscore (2)}0) surface GaN thinfilm by utilizing as the substrate the (11{overscore (2)}0) surfaceAlN/MnS/Si (100) thin films which are obtained by starting from thecommonly used Si substrate, and hence to fabricate the stacked structurewith the cross-sectional structure as shown in FIG. 1. In FIG. 1, thereference numeral 1 designates the single crystal Si (100) substrate; 2designates the MnS layer (of about 50 nm thickness) formed on the singlecrystal substrate 1; 3 designates an AlN layer (of about 1000 nmthickness) formed on the MnS layer 2, and 4 designates a GaN layer (ofabout 100 nm thickness) formed on the AlN layer and functioning as alight emitting layer.

[0071] Such a stacked structure can be formed as described below. Thesingle crystal Si (100) substrate had its native oxide removed by HF(Hydrogen Fluoride), followed by being washed with water, placed in adeposition chamber, and drawn to vacuum for about ten minutes. Then, theMnS buffer layer 2 was formed to a thickness of about 50 nm by the PLDmethod at a substrate temperature of 700° C. in the vacuum of about1×10⁻⁶ Torr. The thin film was cooled at room temperature, and the AlNlayer 3 was formed to a thickness of about 1000 nm at a substratetemperature of 700° C. in a nitrogen atmosphere of about 5×10⁻⁵ Torr inanother PLD system. Then, the GaN layer 4 was formed to about 100 nm atthe substrate temperature of 1000° C. by the MOCVD method.

[0072] FIGS. 9-11 each show a cross-sectional TEM image: FIG. 9 showsthat of the entire cross-section of the GaN/AlN/MnS/Si (100) thin films;FIG. 10 shows that of the AlN/MnS interface; and FIG. 11 shows that ofthe GaN/AlN interface. These figures show little interface reactionlayer, presenting clear lattice images. As a result of the XRDmeasurement, it was found that the GaN thin film with a majororientation (11{overscore (2)}0) was formed.

[0073]FIG. 12 illustrates a cathode luminescence (CL) light emittingspectrum of the GaN/AlN/MnS/Si (100) thin films at room temperature(295K). The light emitting of about 3.3 eV ultraviolet light wasobserved.

[0074] Sulfides other than MnS, which are epitaxially grown on the Sisubstrate, will be enumerated. FIGS. 13 and 14 illustrate 2θ-ωmeasurement results using MgS (FIG. 13) and pole-figure measurementresults of MgS (222) peaks (FIG. 14). FIG. 15 illustrates 2θ-ω)measurement results using CaS. Both the MgS and CaS thin films areepitaxially grown on the Si (100) substrate.

[0075]FIGS. 16A and 16B illustrate XRD measurement results when the (Zn,Mn)S (Mn is 5%) is formed on the Si substrate by the PLD method. It has(100) orientation as illustrated in FIG. 16A when it is formed on the Si(100) substrate, and (111) orientation as illustrated in FIG. 16B whenit is formed on the Si (111) substrate. Accordingly, as in the case offorming an ionic bonding epitaxial thin film on a Si substrate using ZnSas a buffer layer, using (Zn, Mn) S as the buffer layer will make itpossible to epitaxially grow an ionic crystal thin film with a cubicstructure on the Si (100) substrate, and a hexagonal ionic crystal thinfilm on the Si (111) substrate.

[0076] Incidentally, since the lattice constant of ZnS is smaller thanthat of a Si substrate by only 0.5% at room temperature, it is suitablefor epitaxial growth. Using a composite metal sulfide such as (Zn, Mn)S,in which part of Zn is replaced by another metal, can vary the latticeconstant of ZnS slightly, thereby being able to create a compositionwith better lattice matching with Si. In this case, it is preferable touse materials represented by chemical formula Zn(1−x)M_(x)S_(y) (where xand y are values between 0 and 1), in which part of zinc of the zincsulfide (ZnS) is replaced by a particular metal (M). It is alsopreferable to use materials represented by chemical formulaZn(1−x)M_(x)S_(y) (where x and y are values between 0 and 1), in whichpart of zinc of the zinc sulfide (ZnS) is replaced by a particular metal(M). The thermal expansion coefficient of Si is about 4.6×10⁻⁶/K, whichis slightly less than that of ZnS of about 6.7×10⁻⁶/K. Thus, it will bepossible to control the opposite film formation temperature by thecomposition of the sulfide buffer layer.

[0077] Furthermore, the following growing methods are also preferable. Afirst method epitaxially grows a metal sulfide on a single crystalsilicon substrate by supplying a molecular metal sulfide on thesubstrate under a reduced pressure, and then epitaxially grows acompound thin film with ionic bonding thereon. A second methodepitaxially grows a metal sulfide on a single crystal silicon substrateby supplying a molecular metal sulfide on the substrate under a reducedpressure, and then epitaxially grows two or more compound thin filmssequentially with ionic bonding thereon. A third method epitaxiallygrows a metal sulfide on a single crystal silicon substrate by supplyinga molecular manganese sulfide on the substrate under a reduced pressure,and then epitaxially grows aluminum nitride (AlN) with a (11{overscore(2)}0) surface thereon, followed by growing a gallium nitride (GaN) thinfilm with a (11{overscore (2)}0) surface on the aluminum nitride layer.

[0078] A simple metal sulfide whose lattice constant is close to that ofSi is ZnS, and their lattice mismatching is about 0.5%. Accordingly, asfor a sulfide other than ZnS, which has a large lattice mismatching withSi, it will be considered its crystalline is impaired when grown on theSi substrate, thereby degrading the crystalline of an ionic crystal thinfilm formed on its sulfide layer in its initial growing step. However,the crystalline of the ionic crystal thin film can be improved byincreasing its thickness or by controlling its growing conditions. Forexample, a lateral overgrowth method is effective which forms a mask ofsilicon oxide and the like on a substrate crystal with a highdislocation density, and carries out facet formation by starting crystalgrowth from an opening formed by lithography. Thus, it is necessary forthe buffer layer only to determine the orientation of the epitaxialgrowth of the ionic crystal between the thin film formed thereon and theSi substrate as described in the foregoing embodiment.

[0079] Consequently, in spite of a small lattice mismatching with Si,using a buffer layer composed of an epitaxially grown sulfide makes itpossible to form an ionic crystal thin film device on the buffer layerby the epitaxial growth.

[0080] As described above, according to the present invention, using thesulfide buffer layer makes it easy to form the thin film device byepitaxially growing the ionic bonding crystal on the Si substrate withimproving the characteristics. In particular, forming GaN/AlN/MnS/Si(100) thin films enables the commonly used Si substrate to be used toform the GaN (11{overscore (2)}0) surface with the thermodynamicallystable wurtzite structure which is free from the Stark effect on itslight emitting characteristics, thereby being able to form a highlyefficient light emitting device at low cost.

[0081] The present invention has been described in detail with respectto preferred embodiments, and it will now be apparent from the foregoingto those skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspect, and it isthe intention, therefore, in the apparent claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

What is claimed is:
 1. A thin film device comprising: a metal sulfidelayer formed on a single crystal silicon substrate by epitaxial growth;and a compound thin film with ionic bonding, which is formed on themetal sulfide layer by epitaxial growth.
 2. A thin film devicecomprising: a metal sulfide layer formed on a single crystal siliconsubstrate by epitaxial growth; and at least two compound thin films withionic bonding, which are formed on the metal sulfide layer by epitaxialgrowth.
 3. The thin film device as claimed in claim 1, wherein saidmetal sulfide layer is composed of one of a manganese sulfide (MnS),magnesium sulfide (MgS), and calcium sulfide (CaS).
 4. The thin filmdevice as claimed in claim 2, wherein said metal sulfide layer iscomposed of one of a manganese sulfide (MnS), magnesium sulfide (MgS),and calcium sulfide (CaS).
 5. The thin film device as claimed in claim1, wherein said metal sulfide layer is composed of a material whosechemical formula is given by Zn(1−x)M_(x)S_(y), in which part of zinc ofzinc sulfide (ZnS) is substituted by another metal (M), where x and yare values between 0 and
 1. 6. The thin film device as claimed in claim2, wherein said metal sulfide layer is composed of a material whosechemical formula is given by Zn(1−x)M_(x)S_(y), in which part of zinc ofzinc sulfide (ZnS) is substituted by another metal (M), where x and yare values between 0 and
 1. 7. The thin film device as claimed in claim5, wherein said metal sulfide layer is composed of zinc manganesesulfide ((Zn, Mn)S).
 8. The thin film device as claimed in claim 6,wherein said metal sulfide layer is composed of zinc manganese sulfide((Zn, Mn)S).
 9. The thin film device as claimed in claim 1, wherein saidmetal sulfide layer is composed of a material whose chemical formula isgiven by Zn(1−x)(M, N, . . . )_(x)S_(y), in which part of zinc of zincsulfide (ZnS) is substituted by other metals (M, N, . . . ), where x andy are values between 0 and
 1. 10. The thin film device as claimed inclaim 2, wherein said metal sulfide layer is composed of a materialwhose chemical formula is given by Zn(1−x)(M, N, . . . )_(x)S_(y), inwhich part of zinc of zinc sulfide (ZnS) is substituted by other metals(M, N, . . . ), where x and y are values between 0 and
 1. 11. The thinfilm device as claimed in claim 1, further comprising a platinum grouplayer formed between said metal sulfide layer and said compound thinfilm by epitaxial growth.
 12. The thin film device as claimed in claim2, further comprising a platinum group layer formed between said metalsulfide layer and said compound thin film by epitaxial growth.
 13. Thethin film device as claimed in claim 11, wherein a metal of saidplatinum group layer is one of rhodium, iridium, palladium and platinumor an alloy of them, and said platinum group layer is composed of asingle layer or multi-layer thin film thereof.
 14. The thin film deviceas claimed in claim 12, wherein a metal of said platinum group layer isone of rhodium, iridium, palladium and platinum or an alloy of them, andsaid platinum group layer is composed of a single layer or multi-layerthin film thereof.
 15. The thin film device as claimed in claim 1,wherein said compound thin film is composed of a metal nitride thinfilm.
 16. The thin film device as claimed in claim 2, wherein saidcompound thin film is composed of a metal nitride thin film.
 17. Thethin film device as claimed in claim 3, wherein said compound thin filmis composed of a metal nitride thin film.
 18. The thin film device asclaimed in claim 4, wherein said compound thin film is composed of ametal nitride thin film.
 19. The thin film device as claimed in claim 5,wherein said compound thin film is composed of a metal nitride thinfilm.
 20. The thin film device as claimed in claim 6, wherein saidcompound thin film is composed of a metal nitride thin film.
 21. Thethin film device as claimed in claim 7, wherein said compound thin filmis composed of a metal nitride thin film.
 22. The thin film device asclaimed in claim 8, wherein said compound thin film is composed of ametal nitride thin film.
 23. The thin film device as claimed in claim 9,wherein said compound thin film is composed of a metal nitride thinfilm.
 24. The thin film device as claimed in claim 10, wherein saidcompound thin film is composed of a metal nitride thin film.
 25. Thethin film device as claimed in claim 11, wherein said compound thin filmis composed of a metal nitride thin film.
 26. The thin film device asclaimed in claim 12, wherein said compound thin film is composed of ametal nitride thin film.
 27. The thin film device as claimed in claim13, wherein said compound thin film is composed of a metal nitride thinfilm.
 28. The thin film device as claimed in claim 14, wherein saidcompound thin film is composed of a metal nitride thin film.
 29. Thethin film device as claimed in claim 1, wherein said compound thin filmis composed of a metal oxide thin film.
 30. The thin film device asclaimed in claim 2, wherein said compound thin film is composed of ametal oxide thin film.
 31. The thin film device as claimed in claim 3,wherein said compound thin film is composed of a metal oxide thin film.32. The thin film device as claimed in claim 4, wherein said compoundthin film is composed of a metal oxide thin film.
 33. The thin filmdevice as claimed in claim 5, wherein said compound thin film iscomposed of a metal oxide thin film.
 34. The thin film device as claimedin claim 6, wherein said compound thin film is composed of a metal oxidethin film.
 35. The thin film device as claimed in claim 7, wherein saidcompound thin film is composed of a metal oxide thin film.
 36. The thinfilm device as claimed in claim 8, wherein said compound thin film iscomposed of a metal oxide thin film.
 37. The thin film device as claimedin claim 9, wherein said compound thin film is composed of a metal oxidethin film.
 38. The thin film device as claimed in claim 10, wherein saidcompound thin film is composed of a metal oxide thin film.
 39. The thinfilm device as claimed in claim 11, wherein said compound thin film iscomposed of a metal oxide thin film.
 40. The thin film device as claimedin claim 12, wherein said compound thin film is composed of a metaloxide thin film.
 41. The thin film device as claimed in claim 13,wherein said compound thin film is composed of a metal oxide thin film.42. The thin film device as claimed in claim 14, wherein said compoundthin film is composed of a metal oxide thin film.
 43. The thin filmdevice as claimed in claim 1, wherein said compound thin film iscomposed of a metal sulfide thin film.
 44. The thin film device asclaimed in claim 2, wherein said compound thin film is composed of ametal sulfide thin film.
 45. The thin film device as claimed in claim 3,wherein said compound thin film is composed of a metal sulfide thinfilm.
 46. The thin film device as claimed in claim 4, wherein saidcompound thin film is composed of a metal sulfide thin film.
 47. Thethin film device as claimed in claim 5, wherein said compound thin filmis composed of a metal sulfide thin film.
 48. The thin film device asclaimed in claim 6, wherein said compound thin film is composed of ametal sulfide thin film.
 49. The thin film device as claimed in claim 7,wherein said compound thin film is composed of a metal sulfide thinfilm.
 50. The thin film device as claimed in claim 8, wherein saidcompound thin film is composed of a metal sulfide thin film.
 51. Thethin film device as claimed in claim 9, wherein said compound thin filmis composed of a metal sulfide thin film.
 52. The thin film device asclaimed in claim 10, wherein said compound thin film is composed of ametal sulfide thin film.
 53. The thin film device as claimed in claim11, wherein said compound thin film is composed of a metal sulfide thinfilm.
 54. The thin film device as claimed in claim 12, wherein saidcompound thin film is composed of a metal sulfide thin film.
 55. Thethin film device as claimed in claim 13, wherein said compound thin filmis composed of a metal sulfide thin film.
 56. The thin film device asclaimed in claim 14, wherein said compound thin film is composed of ametal sulfide thin film.
 57. A thin film device comprising: a manganesesulfide (MnS) layer formed on a single crystal silicon (100) substrateby epitaxial growth; and an aluminum nitride (AlN) layer formed on saidmanganese sulfide layer by epitaxial growth, said aluminum nitride (AlN)layer having a (11{overscore (2)}0) surface as its top surface.
 58. Thethin film device as claimed in claim 57, further comprising a compoundthin film with ionic bonding, which has a (11{overscore (2)}0) surfaceformed by epitaxial growth as its top surface, and is formed on saidaluminum nitride (AlN) layer having the (11{overscore (2)}0) surface asits top surface, or via another intermediate layer.
 59. The thin filmdevice as claimed in claim 58, wherein said compound thin film iscomposed of a gallium nitride (GaN) thin film having a (11{overscore(2)}0) surface as its top surface.
 60. A fabrication method of a thinfilm device comprising the steps of: epitaxially growing metal sulfideon a single crystal silicon substrate by feeding molecular metal sulfideon the single crystal silicon substrate under a reduced pressure; andepitaxially growing a compound thin film with ionic bonding on the metalsulfide.
 61. A fabrication method of a thin film device comprising thesteps of: epitaxially growing metal sulfide on a single crystal siliconsubstrate by feeding molecular metal sulfide on the single crystalsilicon substrate under a reduced pressure; and epitaxially growing atleast two compound thin films with ionic bonding sequentially on themetal sulfide.
 62. A fabrication method of a thin film device comprisingthe steps of: epitaxially growing a metal sulfide layer on a singlecrystal silicon substrate by feeding molecular manganese sulfide on thesingle crystal silicon substrate under a reduced pressure; epitaxiallygrowing an aluminum nitride (AlN) layer having a (11{overscore (2)}0)surface as its top surface; and forming on said aluminum nitride layer agallium nitride (GaN) thin film having a (11{overscore (2)}0) surface asits top surface.
 63. A fabrication method of a thin film devicecomprising the step of sequentially stacking a metal sulfide layerepitaxially grown on a single crystal silicon substrate, and at leasttwo compound thin films with ionic bonding, which are epitaxially grownon said metal sulfide layer.
 64. A fabrication method of a thin filmdevice comprising the steps of: forming a metal sulfide layer on asingle crystal silicon substrate by epitaxial growth; forming a platinumgroup layer on said metal sulfide layer by epitaxial growth; and forminga compound thin film ionic bonding on said platinum group layer byepitaxial growth.
 65. The fabrication method of a thin film device asclaimed in claim 60, wherein said compound thin film is composed of ametal nitride thin film.
 66. The fabrication method of a thin filmdevice as claimed in claim 61, wherein said compound thin film iscomposed of a metal nitride thin film.
 67. The fabrication method of athin film device as claimed in claim 63, wherein said compound thin filmis composed of a metal nitride thin film.
 68. The fabrication method ofa thin film device as claimed in claim 64, wherein said compound thinfilm is composed of a metal nitride thin film.
 69. The fabricationmethod of a thin film device as claimed in claim 60, wherein saidcompound thin film is composed of a metal oxide thin film.
 70. Thefabrication method of a thin film device as claimed in claim 61, whereinsaid compound thin film is composed of a metal oxide thin film.
 71. Thefabrication method of a thin film device as claimed in claim 63, whereinsaid compound thin film is composed of a metal oxide thin film.
 72. Thefabrication method of a thin film device as claimed in claim 64, whereinsaid compound thin film is composed of a metal oxide thin film.
 73. Thefabrication method of a thin film device as claimed in claim 60, whereinsaid compound thin film is composed of a metal sulfide thin film. 74.The fabrication method of a thin film device as claimed in claim 61,wherein said compound thin film is composed of a metal sulfide thinfilm.
 75. The fabrication method of a thin film device as claimed inclaim 63, wherein said compound thin film is composed of a metal sulfidethin film.
 76. The fabrication method of a thin film device as claimedin claim 64, wherein said compound thin film is composed of a metalsulfide thin film.